Raster scanning for depth detection

ABSTRACT

Techniques are provided for determining distance to an object in a depth camera&#39;s field of view. The techniques may include raster scanning light over the object and detecting reflected light from the object. One or more distances to the object may be determined based on the reflected image. A 3D mapping of the object may be generated. The distance(s) to the object may be determined based on times-of-flight between transmitting the light from a light source in the camera to receiving the reflected image from the object. Raster scanning the light may include raster scanning a pattern into the field of view. Determining the distance(s) to the object may include determining spatial differences between a reflected image of the pattern that is received at the camera and a reference pattern.

CLAIM OF PRIORITY

This application is a continuation application of U.S. patentapplication Ser. No. 12/726,250, entitled “RASTER SCANNING FOR DEPTHDETECTION,” filed Mar. 17, 2010, now U.S. Pat. No. 8,279,418, which isincorporated herein by reference in its entirety.

BACKGROUND

A depth camera system obtains data regarding the location of a human orother object in a physical space. This information may be referred to as“depth information.” The depth information may be input to anapplication in a computing system for a wide variety of applications.Many applications are possible, such as for military, entertainment,sports and medical purposes. For instance, depth information regarding ahuman can be mapped to a three-dimensional (3-D) human skeletal modeland used to create an animated character or avatar.

To determine depth information, a depth camera may project light onto anobject in the camera's field of view. The light reflects off the objectand back to the camera, where it is processed to determine the depthinformation. However, the intensity of the light that is reflected backto the camera may be very weak. Therefore, the signal-to-noise ratio(S/N) may be poor. Furthermore, if part of the object extends out of thecamera's field of view, then the depth of that portion of the objectcannot be determined.

Therefore, further refinements are needed which allow a more accuratedetermination of the depth of objects within a field of view of a depthcamera. One such need is to improve the S/N of the light signal thatreflects from the object. Another need is to provide better control thefield of view.

SUMMARY

A machine-implemented method and system are provided for determiningdepth information for one or more objects within a field of view of adepth camera. The method and system provide for an accuratedetermination of the depth of objects within a field of view of a depthcamera. The method and system may provide for a good S/N of the lightsignal that reflects from the object. The method and system may allowthe depth camera's field of view to be dynamically adjusted.

One embodiment is a machine-implemented method of determining distanceto an object. The method includes transmitting light from a light sourcein a camera. The light is raster scanned over an object in a field ofview of the camera. A reflected image of the light is received from theobject at a detector. One or more distances to the object are determinedbased on the reflected image.

One embodiment is a depth camera that includes a light source thattransmits light, a scanning element in optical communication with thelight source, a light detector, and distance determination logic. Thescanning element raster scans the light over a field of view by scanningin an x-direction and a y-direction. The light detector receives areflected image of the scanned light from an object within the field ofview. The distance determination logic determines a distance ordistances to the object within the field of view based on the reflectedimage.

One embodiment is a machine-implemented method of raster scanning apattern to determine depth information. The method includes transmittinglight from a light source in a camera. A scanning element is controlledwhile transmitting the light to scan a line in a field of view of thecamera. An image from an object in the field of view is received at alinear array detector in the camera. The image corresponds to at least aportion of the scan line. A determination is made whether to scananother line in the pattern. The transmitting, controlling, andreceiving is repeated if another line is to be scanned. Spatialproperties of the received images are analyzed. A distance or distancesto the object within the field of view is determined based on thespatial analysis.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the description.This summary is not intended to identify key features or essentialfeatures of the claimed subject matter, nor is it intended to be used tolimit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example embodiment of a motion capture system.

FIG. 2 depicts an example block diagram of the motion capture system ofFIG. 1.

FIG. 3 depicts an example block diagram of a computing environment thatmay be used in the motion capture system of FIG. 1.

FIG. 4 depicts another example block diagram of a computing environmentthat may be used in the motion capture system of FIG. 1.

FIG. 5A depicts a block diagram of one embodiment of a depth camera thatmay use time-of-flight to determine depth information of a rasterscanned light.

FIG. 5B depicts a block diagram of one embodiment of a depth camera thatuses a structured light pattern to determine depth information.

FIG. 6 is a flowchart of one embodiment of a process of determining adistance to one or more objects in the field of view of a depth camera.

FIG. 7 is a flowchart of one embodiment of a process of scanning apattern in a depth camera's field of view.

FIG. 8A is a flowchart of one embodiment of a process of determining oneor more distances to an object in the camera's field of view based ontime-of-flight.

FIG. 8B is a flowchart of one embodiment of a process of determining oneor more distances to an object in the camera's field of view based onspatial analysis of a received image.

FIG. 9 is a flowchart of one embodiment of a process of generating areference image

DETAILED DESCRIPTION

Techniques are provided for determining one or more distances to anobject (or objects) in a depth camera's field of view. The techniquesmay include raster scanning light over an object in a field of view ofthe camera. An image of the light that reflects from the object isreceived at the camera. One or more distances to the object aredetermined based on the reflected image. In one embodiment, a 3D mappingof one or more objects in the field of view is generated.

In one embodiment, determining the distance(s) to the object includesdetermining times-of-flight between transmitting the light from a lightsource in the camera to receiving the reflected image from the object.Separate time-of-flight information may be determined for differentpoints in the raster scan. Therefore, a 3D mapping of the object couldbe determined.

In one embodiment, raster scanning the light includes raster scanning apattern into the field of view. Determining the distance(s) to theobject may include determining spatial differences between a reflectedimage of the pattern that is received at the camera and a referencepattern. The pattern that is scanned into the field of view may be aknown pattern such as a grid or any other known pattern. The referencepattern may be an image that would result by raster scanning the patternover a reference object at a known distance from the depth camera.

One possible use of collecting depth information of one or more objectswithin a field of view of a depth camera is to input the depthinformation to a motion capture system. However, it will be understoodthat the depth information is not limited to a motion capture system.For purposes of illustration, an example motion capture system 10 willbe described. FIG. 1 depicts an example embodiment of a motion capturesystem 10 in which a person interacts with an application. The motioncapture system 10 includes a display 196, a depth camera system 20, anda computing environment or apparatus 12. The depth camera system 20 mayinclude an image camera component 22 having a depth detection lighttransmitter 24, depth detection light receiver 25, and a red-green-blue(RGB) camera 28. In one embodiment, the depth detection lighttransmitter 24 emits a collimated light beam. An example of collimatedlight includes, but is not limited to, Infrared (IR) laser. In oneembodiment, the depth detection light component is an LED. Light thatreflects off from an object 8 in the field of view is detected by thedepth detection light receiver 25.

A user, also referred to as a person or player, stands in a field ofview 6 of the depth camera system 20. Lines 2 and 4 denote a boundary ofthe field of view 6. In this example, the depth camera system 20, andcomputing environment 12 provide an application in which an avatar 197on the display 196 track the movements of the object 8 (e.g., a user)For example, the avatar 197 may raise an arm when the user raises anarm. The avatar 197 is standing on a road 198 in a 3-D virtual world. ACartesian world coordinate system may be defined which includes a z-axiswhich extends along the focal length of the depth camera system 20,e.g., horizontally, a y-axis which extends vertically, and an x-axiswhich extends laterally and horizontally. Note that the perspective ofthe drawing is modified as a simplification, as the display 196 extendsvertically in the y-axis direction and the z-axis extends out from thedepth camera system 20, perpendicular to the y-axis and the x-axis, andparallel to a ground surface on which the user stands.

Generally, the motion capture system 10 is used to recognize, analyze,and/or track an object. The computing environment 12 can include acomputer, a gaming system or console, or the like, as well as hardwarecomponents and/or software components to execute applications.

The depth camera system 20 may include a camera which is used tovisually monitor one or more objects 8, such as the user, such thatgestures and/or movements performed by the user may be captured,analyzed, and tracked to perform one or more controls or actions withinan application, such as animating an avatar or on-screen character orselecting a menu item in a user interface (UI).

The motion capture system 10 may be connected to an audiovisual devicesuch as the display 196, e.g., a television, a monitor, ahigh-definition television (HDTV), or the like, or even a projection ona wall or other surface, that provides a visual and audio output to theuser. An audio output can also be provided via a separate device. Todrive the display, the computing environment 12 may include a videoadapter such as a graphics card and/or an audio adapter such as a soundcard that provides audiovisual signals associated with an application.The display 196 may be connected to the computing environment 12 via,for example, an S-Video cable, a coaxial cable, an HDMI cable, a DVIcable, a VGA cable, or the like.

The object 8 may be tracked using the depth camera system 20 such thatthe gestures and/or movements of the user are captured and used toanimate an avatar or on-screen character and/or interpreted as inputcontrols to the application being executed by computer environment 12.

Some movements of the object 8 may be interpreted as controls that maycorrespond to actions other than controlling an avatar. For example, inone embodiment, the player may use movements to end, pause, or save agame, select a level, view high scores, communicate with a friend, andso forth. The player may use movements to select the game or otherapplication from a main user interface, or to otherwise navigate a menuof options. Thus, a full range of motion of the object 8 may beavailable, used, and analyzed in any suitable manner to interact with anapplication.

The person can hold an object such as a prop when interacting with anapplication. In such embodiments, the movement of the person and theobject may be used to control an application. For example, the motion ofa player holding a racket may be tracked and used for controlling anon-screen racket in an application which simulates a tennis game. Inanother example embodiment, the motion of a player holding a toy weaponsuch as a plastic sword may be tracked and used for controlling acorresponding weapon in the virtual world of an application whichprovides a pirate ship.

The motion capture system 10 may further be used to interpret targetmovements as operating system and/or application controls that areoutside the realm of games and other applications which are meant forentertainment and leisure. For example, virtually any controllableaspect of an operating system and/or application may be controlled bymovements of the object 8.

FIG. 2 depicts an example block diagram of the motion capture system 10of FIG. 1 a. The depth camera system 20 may be configured to capturevideo with depth information including a depth image that may includedepth values. Technique for determining depth values by illuminating anobject using raster scanning are described herein. The depth camerasystem 20 may organize the depth information into “Z layers,” or layersthat may be perpendicular to a Z-axis extending from the depth camerasystem 20 along its line of sight.

The depth camera system 20 may include an image camera component 22,such as a depth camera that captures the depth image of a scene in aphysical space. The image camera component 22 may include a depthdetection light transmitter 24 and a depth detection light receiver 25to capture depth information. For example, depth camera system 20 mayuse the depth detection light transmitter 24 to emit light onto thephysical space and use depth detection light receiver 25 to detect thereflected light from the surface of one or more objects in the physicalspace.

In some embodiments, the depth detection light transmitter 24 transmitspulsed infrared light such that the time between an outgoing light pulseand a corresponding incoming light pulse may be measured and used todetermine a physical distance from the depth camera system 20 to aparticular location on the objects in the physical space. The phase ofthe outgoing light wave may be compared to the phase of the incominglight wave to determine a phase shift. Note that the transmitted lightmay be modulated to assist in determining the phase difference. Thephase shift of the modulated light may then be used to determine aphysical distance from the depth camera system 20 to a particularlocation on the targets or objects.

In another example embodiment, the depth camera system 20 may usestructured light to capture depth information. In such an analysis,patterned light (e.g., a known pattern such as grid pattern or a stripepattern) may be projected onto the scene via, for example, the depthdetection light transmitter 24. The pattern that is received at thedepth detection light receiver 25 may be analyzed to determine depthinformation. In one embodiment, the pattern is spatially analyzed. Inone embodiment, the pattern is analyzed for apparent deformations. Thatis, the received pattern may appear deformed, as compared to a referencepattern, based on the distance of the object from the camera.

The red-green-blue (RGB) camera 28 may be used to capture an image. Thedepth information may be merged with the image from the RGB camera 28 inorder to create a depth image.

The depth camera system 20 may further include a microphone 30 whichincludes, e.g., a transducer or sensor that receives and converts soundwaves into an electrical signal. Additionally, the microphone 30 may beused to receive audio signals such as sounds that are provided by aperson to control an application that is run by the computingenvironment 12. The audio signals can include vocal sounds of the personsuch as spoken words, whistling, shouts and other utterances as well asnon-vocal sounds such as clapping hands or stomping feet.

The depth camera system 20 may include a processor 32 that is incommunication with the image camera component 22. The processor 32 mayinclude a standardized processor, a specialized processor, amicroprocessor, or the like that may execute instructions including, forexample, instructions for determining a depth image, which will bedescribed in more detail below.

The depth camera system 20 may further include a memory component 34that may store instructions that are executed by the processor 32, aswell as storing images or frames of images captured by the RGB camera,or any other suitable information, images, or the like. According to anexample embodiment, the memory component 34 may include random accessmemory (RAM), read only memory (ROM), cache, Flash memory, a hard disk,or any other suitable tangible computer readable storage component. Thememory component 34 may be a separate component in communication withthe image capture component 22 and the processor 32 via a bus 21.According to another embodiment, the memory component 34 may beintegrated into the processor 32 and/or the image capture component 22.

The depth camera system 20 may be in communication with the computingenvironment 12 via a communication link 36. The communication link 36may be a wired and/or a wireless connection. According to oneembodiment, the computing environment 12 may provide a clock signal tothe depth camera system 20 via the communication link 36 that indicateswhen to capture image data from the physical space which is in the fieldof view of the depth camera system 20.

Additionally, the depth camera system 20 may provide the depthinformation and images captured by the RGB camera 28 to the computingenvironment 12 via the communication link 36. The computing environment12 may then use the depth information, and captured images to control anapplication. For example, as shown in FIG. 2, the computing environment12 may include a gestures library 190, such as a collection of gesturefilters, each having information concerning a gesture that may beperformed (as the user moves). For example, a gesture filter can beprovided for various hand gestures, such as swiping or flinging of thehands. By comparing a detected motion to each filter, a specifiedgesture or movement which is performed by a person can be identified. Anextent to which the movement is performed can also be determined.

The computing environment may also include a processor 192 for executinginstructions which are stored in a memory 194 to provide audio-videooutput signals to the display device 196 and to achieve otherfunctionality as described herein.

FIG. 3 depicts an example block diagram of a computing environment thatmay be used in the motion capture system of FIG. 1. The computingenvironment can be used to determine distances to objects in the fieldof view of a depth camera based on depth information. The computingenvironment such as the computing environment 12 described above mayinclude a multimedia console 100, such as a gaming console. Themultimedia console 100 has a central processing unit (CPU) 101 having alevel 1 cache 102, a level 2 cache 104, and a flash ROM (Read OnlyMemory) 106. The level 1 cache 102 and a level 2 cache 104 temporarilystore data and hence reduce the number of memory access cycles, therebyimproving processing speed and throughput. The CPU 101 may be providedhaving more than one core, and thus, additional level 1 and level 2caches 102 and 104. The memory 106 such as flash ROM may storeexecutable code that is loaded during an initial phase of a boot processwhen the multimedia console 100 is powered on.

A graphics processing unit (GPU) 108 and a video encoder/video codec(coder/decoder) 114 form a video processing pipeline for high speed andhigh resolution graphics processing. Data is carried from the graphicsprocessing unit 108 to the video encoder/video codec 114 via a bus. Thevideo processing pipeline outputs data to an A/V (audio/video) port 140for transmission to a television or other display. A memory controller110 is connected to the GPU 108 to facilitate processor access tovarious types of memory 112, such as RAM (Random Access Memory).

The multimedia console 100 includes an I/O controller 120, a systemmanagement controller 122, an audio processing unit 123, a networkinterface 124, a first USB host controller 126, a second USB controller128 and a front panel I/O subassembly 130 that may be implemented on amodule 118. The USB controllers 126 and 128 serve as hosts forperipheral controllers 142(1)-142(2), a wireless adapter 148, and anexternal memory device 146 (e.g., flash memory, external CD/DVD ROMdrive, removable media, etc.). The network interface (NW IF) 124 and/orwireless adapter 148 provide access to a network (e.g., the Internet,home network, etc.) and may be any of a wide variety of various wired orwireless adapter components including an Ethernet card, a modem, aBluetooth module, a cable modem, and the like.

System memory 143 is provided to store application data that is loadedduring the boot process. A media drive 144 is provided and may comprisea DVD/CD drive, hard drive, or other removable media drive. The mediadrive 144 may be internal or external to the multimedia console 100.Application data may be accessed via the media drive 144 for execution,playback, etc. by the multimedia console 100. The media drive 144 isconnected to the I/O controller 120 via a bus, such as a Serial ATA busor other high speed connection.

The system management controller 122 provides a variety of servicefunctions related to assuring availability of the multimedia console100. The audio processing unit 123 and an audio codec 132 form acorresponding audio processing pipeline with high fidelity and stereoprocessing. Audio data is carried between the audio processing unit 123and the audio codec 132 via a communication link. The audio processingpipeline outputs data to the A/V port 140 for reproduction by anexternal audio player or device having audio capabilities.

The front panel I/O subassembly 130 supports the functionality of thepower button 150 and the eject button 152, as well as any LEDs (lightemitting diodes) or other indicators exposed on the outer surface of themultimedia console 100. A system power supply module 136 provides powerto the components of the multimedia console 100. A fan 138 cools thecircuitry within the multimedia console 100.

The CPU 101, GPU 108, memory controller 110, and various othercomponents within the multimedia console 100 are interconnected via oneor more buses, including serial and parallel buses, a memory bus, aperipheral bus, and a processor or local bus using any of a variety ofbus architectures.

When the multimedia console 100 is powered on, application data may beloaded from the system memory 143 into memory 112 and/or caches 102, 104and executed on the CPU 101. The application may present a graphicaluser interface that provides a consistent user experience whennavigating to different media types available on the multimedia console100. In operation, applications and/or other media contained within themedia drive 144 may be launched or played from the media drive 144 toprovide additional functionalities to the multimedia console 100.

The multimedia console 100 may be operated as a standalone system byconnecting the system to a television or other display. In thisstandalone mode, the multimedia console 100 allows one or more users tointeract with the system, watch movies, or listen to music. However,with the integration of broadband connectivity made available throughthe network interface 124 or the wireless adapter 148, the multimediaconsole 100 may further be operated as a participant in a larger networkcommunity.

When the multimedia console 100 is powered on, a specified amount ofhardware resources are reserved for system use by the multimedia consoleoperating system. These resources may include a reservation of memory(e.g., 16 MB), CPU and GPU cycles (e.g., 5%), networking bandwidth(e.g., 8 kbs), etc. Because these resources are reserved at system boottime, the reserved resources do not exist from the application's view.

In particular, the memory reservation may be large enough to contain thelaunch kernel, concurrent system applications and drivers. The CPUreservation is may be constant such that if the reserved CPU usage isnot used by the system applications, an idle thread will consume anyunused cycles.

With regard to the GPU reservation, lightweight messages generated bythe system applications (e.g., popups) are displayed by using a GPUinterrupt to schedule code to render popup into an overlay. The amountof memory for an overlay may depend on the overlay area size and theoverlay may scale with screen resolution. Where a full user interface isused by the concurrent system application, it is preferable to use aresolution independent of application resolution. A scaler may be usedto set this resolution such that the need to change frequency and causea TV resynch is eliminated.

After the multimedia console 100 boots and system resources arereserved, concurrent system applications execute to provide systemfunctionalities. The system functionalities are encapsulated in a set ofsystem applications that execute within the reserved system resourcesdescribed above. The operating system kernel identifies threads that aresystem application threads versus gaming application threads. The systemapplications may be scheduled to run on the CPU 101 at predeterminedtimes and intervals in order to provide a consistent system resourceview to the application. The scheduling is to minimize cache disruptionfor the gaming application running on the console.

When a concurrent system application requires audio, audio processing isscheduled asynchronously to the gaming application due to timesensitivity. A multimedia console application manager (described below)controls the gaming application audio level (e.g., mute, attenuate) whensystem applications are active.

Input devices (e.g., controllers 142(1) and 142(2)) are shared by gamingapplications and system applications. The input devices are not reservedresources, but are to be switched between system applications and thegaming application such that each will have a focus of the device. Theapplication manager may control the switching of input stream, withoutknowledge the gaming application's knowledge and a driver maintainsstate information regarding focus switches. The console 100 may receiveadditional inputs from the depth camera system 20 of FIG. 2, includingthe camera 28.

FIG. 4 depicts another example block diagram of a computing environmentthat may be used in the motion capture system of FIG. 1. The computingenvironment can be used to determine distances to objects in the fieldof view of a depth camera based on depth information. The computingenvironment 220 comprises a computer 241, which typically includes avariety of tangible computer readable storage media. This can be anyavailable media that can be accessed by computer 241 and includes bothvolatile and nonvolatile media, removable and non-removable media. Thesystem memory 222 includes computer storage media in the form ofvolatile and/or nonvolatile memory such as read only memory (ROM) 223and random access memory (RAM) 260. A basic input/output system 224(BIOS), containing the basic routines that help to transfer informationbetween elements within computer 241, such as during start-up, istypically stored in ROM 223. RAM 260 typically contains data and/orprogram modules that are immediately accessible to and/or presentlybeing operated on by processing unit 259. A graphics interface 231communicates with a GPU 229. By way of example, and not limitation, FIG.4 depicts operating system 225, application programs 226, other programmodules 227, and program data 228.

The computer 241 may also include other removable/non-removable,volatile/nonvolatile computer storage media, e.g., a hard disk drive 238that reads from or writes to non-removable, nonvolatile magnetic media,a magnetic disk drive 239 that reads from or writes to a removable,nonvolatile magnetic disk 254, and an optical disk drive 240 that readsfrom or writes to a removable, nonvolatile optical disk 253 such as a CDROM or other optical media. Other removable/non-removable,volatile/nonvolatile tangible computer readable storage media that canbe used in the exemplary operating environment include, but are notlimited to, magnetic tape cassettes, flash memory cards, digitalversatile disks, digital video tape, solid state RAM, solid state ROM,and the like. The hard disk drive 238 is typically connected to thesystem bus 221 through an non-removable memory interface such asinterface 234, and magnetic disk drive 239 and optical disk drive 240are typically connected to the system bus 221 by a removable memoryinterface, such as interface 235.

The drives and their associated computer storage media discussed aboveand depicted in FIG. 4, provide storage of computer readableinstructions, data structures, program modules and other data for thecomputer 241. For example, hard disk drive 238 is depicted as storingoperating system 258, application programs 257, other program modules256, and program data 255. Note that these components can either be thesame as or different from operating system 225, application programs226, other program modules 227, and program data 228. Operating system258, application programs 257, other program modules 256, and programdata 255 are given different numbers here to depict that, at a minimum,they are different copies. A user may enter commands and informationinto the computer 241 through input devices such as a keyboard 251 andpointing device 252, commonly referred to as a mouse, trackball or touchpad. Other input devices (not shown) may include a microphone, joystick,game pad, satellite dish, scanner, or the like. These and other inputdevices are often connected to the processing unit 259 through a userinput interface 236 that is coupled to the system bus, but may beconnected by other interface and bus structures, such as a parallelport, game port or a universal serial bus (USB). The depth camera system20 of FIG. 2, including camera 28, may define additional input devicesfor the console 100. A monitor 242 or other type of display is alsoconnected to the system bus 221 via an interface, such as a videointerface 232. In addition to the monitor, computers may also includeother peripheral output devices such as speakers 244 and printer 243,which may be connected through a output peripheral interface 233.

The computer 241 may operate in a networked environment using logicalconnections to one or more remote computers, such as a remote computer246. The remote computer 246 may be a personal computer, a server, arouter, a network PC, a peer device or other common network node, andtypically includes many or all of the elements described above relativeto the computer 241, although only a memory storage device 247 has beendepicted in FIG. 4. The logical connections include a local area network(LAN) 245 and a wide area network (WAN) 249, but may also include othernetworks. Such networking environments are commonplace in offices,enterprise-wide computer networks, intranets and the Internet.

When used in a LAN networking environment, the computer 241 is connectedto the LAN 245 through a network interface or adapter 237. When used ina WAN networking environment, the computer 241 typically includes amodem 250 or other means for establishing communications over the WAN249, such as the Internet. The modem 250, which may be internal orexternal, may be connected to the system bus 221 via the user inputinterface 236, or other appropriate mechanism. In a networkedenvironment, program modules depicted relative to the computer 241, orportions thereof, may be stored in the remote memory storage device. Byway of example, and not limitation, FIG. 4 depicts remote applicationprograms 248 as residing on memory device 247. It will be appreciatedthat the network connections shown are exemplary and other means ofestablishing a communications link between the computers may be used.

FIG. 5A depicts a block diagram of one embodiment of a depth camerasystem 20. In one embodiment, the depth camera system 20 of FIG. 5Adetermines distance based on time-of-flight of raster scanned light. Thedepth camera system 20 may be used in the example motion capture system10 of FIG. 1; however, it may be used in other systems. The depth camerasystem 20 has a light source 524, a beam splitter 506, a rotatingscanning element 508, a detector 504 a, processing logic 532 and storage534. Together, the light source 524, the beam splitter 506, and thescanning element 508 form the depth detection light transmitter 24. Thedetector 504 a is one embodiment of a depth detection light receiver 25of the device of FIG. 2.

In one embodiment, the light source 524 emits a collimated light beam.The light source 524 may emit Infrared laser, among other light beams.In one embodiment, the light source 524 emits a sequence of pulses oflight. The sequence may be encoded or modulated in way that assistsdetermining time-of-flight. For example, time-of-flight may bedetermined based on a phase difference between the transmitted modulatedlight and received light. In one embodiment, the light source 524 is apoint source. The light is transmitted through the beam splitter 506onto the scanning element 508. Note that the beam splitter 506 is anoptional component that may help to reduce the number of components.

In one embodiment, the scanning element 508 has one or more surfaces 509that reflect light. In one embodiment, the scanning element 508 rotatesunder control of processing logic 532. In one embodiment, the scanningelement 508 rotates such that the light from light source 524 scans overthe field of view in the x-direction and the y-direction. Note that thescanning element 508 may include more than one rotating element. Forexample, one element may rotate as depicted in FIG. 5A to scan in thex-direction, and a second element may rotate into and out of the page ofFIG. 5A. Techniques for two-dimensional raster scanning are well-knownto those of ordinary skill in the art. The x-component of the field ofview is depicted by lines 2, 4. Note that there is also a y-component tothe field of view (not depicted in FIG. 5A).

A circular arrow is depicted on the scanning element 508 to show anexample direction of rotation. The direction may be clockwise instead.The solid arrows depict the light path that corresponds to the depictedposition of the scanning element 508. The dashed arrows correspond tolight paths that correspond to positions of the scanning element 508when it has rotated to other angles. Thus, the dashed arrows correspondto a different point in time. Note that although the scanning element508 is depicted as a rotating element with multiple surfaces other typesof scanning elements may be used.

In one embodiment, the scanning element 508 is capable of scanningmultiple lines in the x-direction, each with a different y-position.After scanning one line in the x-direction, the scanning element 508 iscontrolled in a way that scans a second line at a new y-position. Forexample, the scanning element 508 may be rotated in a direction that isin-and-out of the page of FIG. 5B. Note that the lines are notnecessarily continuous. Many different scan paths can be used. Furtherdetails are discussed below.

Light that reflects off from the one or more objects 8 in the field ofview is captured by the detector 504 a. In this example, the lightreflects off from the object 8 and back to the scanning element 508 (asdepicted by the double arrows). The light then travels back to the beamsplitter 506 and then to the detector 504 a. As previously mentioned,the beam splitter 506 is not a requirement. The detector 504 a may befor example, a CMOS detector, photodiode detector, or a Charge CoupledDevice (CCD). In one embodiment, the data the detector 504 a collects isanalyzed as a single data point. As the raster scanning proceeds toilluminate a new portion of the object 8, additional data may becollected by the detector 504 a.

In the embodiment depicted in FIG. 5A, the axis of illumination isaligned with the image axis. This is depicted by the double-headedarrows between the scanning element 508 and the object. The axis ofillumination is indicated by the arrowhead near the object 8. The imageaxis is indicated by the arrowhead near the scanning element 508. Inother embodiments, the axis of illumination is not aligned with theimage axis.

The processing logic 532 is able to determine distance to the object 8based on the image captured by the detector 504 a. In one embodiment,the distance to the object 8 is determined based on the time-of-flightbetween transmitting the light from the source 524 to receiving thereflected image at the detector 504 a. Note that since the light fromthe source 524 is being scanned across the field of view that thedetector 504 a will collect numerous separate data points thatcorrespond to different x- and y-positions in the field of view.

In one embodiment, the processing logic 532 is a processor that executesinstructions that are stored in memory such as storage 534. However, theprocessing logic 532 can be implemented in whole or in part withhardware. In one embodiment, the processing logic 532 includes anApplication Specific Integrated Circuit (ASIC). Note that the storage534 could be addressable memory such as RAM, ROM, registers, etc.However, the storage 534 could also includes non-addressable storage.For example, the storage 534 may include latches that are notnecessarily addressable by a processor.

FIG. 5B depicts a block diagram of one embodiment of a depth camera 20that may use a light pattern to determine depth information. Thisembodiment is different from FIG. 5A in that it has a linear arraydetector 504 b instead of detector 504 a. Thus, the linear arraydetector 504 b is one embodiment of the depth detection light receiver25 of the device of FIG. 2. As with the embodiment of FIG. 5A, rasterscanning is used to illuminate an object 8 in the field of view.However, in this case, a pattern is raster scanned into the field ofview. The pattern may be spatially analyzed to determine depthinformation. For example, depth information may be determined based ondeformation or warping in the reflected pattern. Note that this may bean apparent deformation based on the vantage point of the linear arraydetector 504 b.

The depth camera 20 may be used in the example motion capture system 10of FIG. 1; however, it may be used in other systems. The depth camera 20has a light source 524, a beam splitter 506, a rotating scanning element508, linear array detector 504 b, processing logic 532, and storage.Together, the light source 524, the beam splitter 506, and the scanningelement 508 form the depth detection light transmitter 24. The lineararray detector 504 b is one embodiment of a depth detection lightreceiver 25.

In one embodiment, the light source 524 emits a collimated light beam.The light source 524 may emit Infrared laser, among other light beams.In one embodiment, the light source 524 emits a sequence of pulses oflight. In one embodiment, the light source 524 is a point source. Thelight is transmitted through the beam splitter 506 onto the scanningelement 508.

The scanning element 508 may be similar to the one in FIG. 5A and willnot be discussed in detail. In this embodiment, the scanning element 508is used to project a pattern into the field of view. Therefore, thepattern may be projected onto whatever objects 8 may be in the field ofview. In one embodiment, the pattern is a known pattern, such as gridpattern or a stripe pattern. Note that because the pattern is beingraster scanned across the field of view, only one point of the patternis being projected at any one time. This allows for a very high S/N asall of the energy may be concentrated on a small point. Stated anotherway, only a portion of the pattern is being projected at any one time.

Light that reflects off from the one or more objects 8 in the field ofview is captured by the linear array detector 504 b. In this example,the light reflects off from the object 8 and back to the scanningelement 508 (as depicted by the double arrows). The light then travelsback to the beam splitter 506 and then to the detector 504 b. Note thatthe linear array detector 504 b may collect many data points. Forexample, the linear array detector 504 b may collect many points for ascan line. After the scanning element 508 is moved to scan a new line ata different y-position, the linear array detector 504 b may be used tocollect a new set of data points. The linear array detector 504 b may befor example, a CMOS detector, photodiode detector, or a CCD. In oneembodiment, the linear array detector 504 b is able to detect light overa linear region.

Therefore, the linear array detector 504 b collects a reflected imagethat is due to the pattern projected onto the object. The distance theobject 8 is from the camera may have an impact on the received pattern.For example, one could consider projecting the pattern onto a referenceobject 8 at a known distance from the camera. If that same pattern isprojected onto an object 8 at a different distance from the camera, thepattern may appear to be “warped” or “deformed.” In one embodiment, theparallax affect is taken advantage of to cause the pattern to appear todeform from the vantage point of the linear array detector 504 b. Thenature and amount of the deformation may be analyzed to determine thedistance to the object. In one embodiment, a z-direction mapping of theobject 8 may be made. That is, for each x- and y-position scan points, az-position may be determined. Thus, the processing logic 532 is able todetermine distance to the object 8 based on the image captured by thelinear array detector 504 b.

In the embodiment depicted in FIG. 5B, the axis of illumination isaligned with the image axis. This is depicted by the double-headedarrows between the scanning element 508 and the object. The axis ofillumination is indicated by the arrowhead near the object. The imageaxis is indicated by the arrowhead near the scanning element 508. Inother embodiments that use a linear array detector 504 b, the axis ofillumination is not aligned with the image axis.

FIG. 6 is a flowchart of one embodiment of a process 600 of determininga distance to one or more objects 8 in the field of view of a depthcamera. The process 600 may used in the depth camera of any of FIG. 5Aor 5B. However, process 600 is not limited to those embodiments.

In step 602, light is transmitted from a light source 524 in a depthcamera 20. For example, the light source 524 in any of the depth cameras20 of FIGS. 5A-5B transmits light. The light may be collimated. In oneembodiment, the light is Infrared. In one embodiment, the light is alaser beam. On one embodiment, the light source 524 emits pulses oflight. In one embodiment, the pulses are structured such that a knownpattern can be raster scanned over the camera's field of view.

In step 604, the light is raster scanned over an object 8 in the fieldof view of the camera. In one embodiment, light from light source 524 isreflected off the scanning element 508 to cause a known pattern to beraster scanned in the camera's field of view. The pattern can be anyknown pattern. In some embodiments, the pattern is irregular such thatdifferent portions of the pattern have unique sub-patterns. In otherwords, different portions of the pattern may be unique from each other.Note that by raster scanning the pattern that the entire pattern is nottransmitted at the same time.

In step 606, a reflected image of the light is received at a lightdetector 504. The light detector 504 could be a point detector 504 a ora linear array detector 504 b. Note that the light is received over aperiod of time. For example, as the scanning element 508 raster scansthe light over the field of view, the detector 504 detects successiveportions of the light over time.

In step 608, one or more distances to the object 8 are determined basedon the reflected image. In one embodiment, the one or more distances aredetermined based on time-of-flight information. In one embodiment, theone or more distances are determined based on spatial analysis of thereceived image or images. In one embodiment, the one or more distancesare determined based on apparent deformation of in the received pattern.

FIG. 7 is a flowchart of one embodiment of a process 700 of scanning aknown pattern into a depth camera's field of view. The known pattern canbe essentially any pattern such that the received image can be analyzedfor apparent deformations in the pattern to determine distance. Process700 is one embodiment of steps 602-604. Note that, in operation, process700 may be repeated over and over to scan the pattern again (or to scana different pattern). Scanning a known pattern may be used inembodiments in which depth is determined based on apparent deformationof the reflected image of the pattern. However, note that embodimentsthat determine depth based on time-of-flight may also scan a knownpattern.

In step 702, data for scanning a line of the pattern is determined. Thedata may include a sequence of pulses for the light source 524 and howto control the scanning element 508 to scan a line. In one embodiment,the storage 534 stores the data such that step 702 is performed byaccessing an appropriate memory address.

In step 704, light for one line of the pattern is transmitted from thelight source 524 while the scanning element 508 is controlled to scanthe line into the field of view. Note scanning a line does not requirethat a continuous path is illuminated. Rather, the scan line may haveportions that are illuminated separated by portions that are notilluminated. The light source 524 may be pulsed to generate such a scanline. However, the scan line may be a continuous path. In oneembodiment, the scan line is approximately horizontal in the field ofview. Note that the scan line could be slightly diagonal such that they-position changes slightly across the scan line. However, note that thescan line may be in any orientation. For example, the scan line could bediagonal such that it goes from upper left to lower right in the fieldof view. The scan line could be more or less vertical, if desired. Also,the scan line is not required to be a straight line. Thus, in someembodiments, the scan line is curved.

Step 706 is a determination of whether a new line is to be scanned. Inone embodiment, the scan line is a predetermined length. For example, ascan line may correspond to a pre-determined angle of rotation of thescanning element 508. Note that this may result in a pre-determinedfield of view. Also, a scan line may correspond to a pre-determinednumber of light pulses. However, neither the angle of rotation nor thenumber of light pulses needs to be pre-determined. In one embodiment,the length of the line being scanned is dynamically adaptable.Therefore, the field of view is dynamically adaptable by varying a rangeover which raster scanning is performed. For example, there might be adefault field of view that can be expanded or narrowed. As oneparticular example, the field of view can be dynamically narrowed if itis determined that the object 8 of interest has already been scanned. Asanother particular example, the field of view can be dynamicallyexpanded if it is determined that the object 8 of interest has not yetbeen fully scanned. For example, of the object 8 of interest is a user'shand, the field of view can be altered to more efficiently capture depthinformation regarding the hand.

Once it is determined that a new line is to be scanned, data for thenext line are determined (step 702). Again, the storage 534 may beaccessed to determine the next set of data. Process 700 continues byscanning more lines until it is determined in step 708 that all lineshave been scanned. The number of scan lines may be pre-determined ordynamically adjustable. Note that dynamically adjusting the number oflines allows the field of view to be dynamically adjusted. A factor fordetermining whether more lines are to be scanned may include whether anobject 8 of interest has been fully scanned.

Note that one variation of process 700 is to scan lines without scanningany particular pattern. For example, embodiments that determine depthbased on time-of-flight do not require any particular pattern to bescanned.

FIG. 8A is a flowchart of one embodiment of a process 800 of determiningone or more distances to an object 8 in the camera's field of view.Process 800 is one embodiment of step 608 of process 600. In thisembodiment, the determination is made based on time-of-flightinformation. In some embodiments, the depth camera of FIG. 5A may useprocess 800. However, other depth cameras described herein are notprecluded from using process 800. In step 802, a time of flight betweentransmitting light from the light source 524 until the light is receivedby the detector 504 is determined. This calculation may be performed forone portion of the raster scan. For example, the calculation may be forone pulse of light.

In one embodiment, the comparison is of the difference in phase betweenthe transmitted light and the received image. For example, the lightsource may be a laser beam that is modulated at a certain frequency. Thedifference in phase between the modulated transmitted laser beam and thereceived image can be used to determine the distance to the object 8.Specifically, the distance can be determined based on the amount ofphase difference and the modulation frequency.

In one embodiment, the comparison is a direct measurement of thedifference in time between transmitting the light and receiving theimage. For example, the light source 524 sends out a short pulse oflight. When the detector 504 receives the light pulse, circuitrycalculates a very precise time difference between transmission andreception. The distance can be determined based on the time differenceand the light frequency.

In step 804, the distance measurement is stored in association with anindicator of what portion of the field of view was being studied. Theprocess 800 continues to process more data by studying additional partsof the raster scan until all portions of the scan are analyzed, asdetermined in step 806. In optional step 808, a 3D map of the object 8is generated based on the data stored in step 804.

FIG. 8B is a flowchart of one embodiment of a process 850 of determiningone or more distances to an object 8 in the camera's field of view. Insome embodiments, the depth camera of FIG. 5B may use process 800.However, other depth cameras 20 described herein are not precluded fromusing process 800. Process 850 is one embodiment of step 608 of process600. In this embodiment, the determination is made based on spatialinformation about a received pattern. For example, the amount by whichthe pattern appears to deform may be used to determine distance.

In step 852, the light that was received at the linear array detector504 b is analyzed. This data may correspond to all of the scan lines orany subset of the scan lines. Note that the limited size of the object 8means that only a portion of the pattern might be returned. However, thepattern can be constructed in a manner such that analysis of only asmall portion of the pattern allows the distance to the object 8 to bedetermined. In one embodiment, the parallax affect is used to determinedepth information. For example, the detector 504 may be off axis fromthe light transmitter such that the parallax affect causes an apparentdeformation of the pattern from the vantage point of the detector 504.However, determining the depth information based on deformation of thepattern is not limited to the parallax affect.

In one embodiment, the depth information is determined by comparing thereceived image of the pattern with one or more reference images. Eachreference image may correspond to a different distance from the camera.Further details of generating reference images are discussed inconnection with FIG. 9. As noted the received image may appear to bedeformed by an amount that corresponds to the distance from the camera.Each reference image may contain the amount and nature of deformationfor a given distance. By comparing the received image to the referenceimages depth may be determined. Note that it is not required that theentire received image be compared with a given reference image. Forexample, the received image can be broken into different pieces, whichare each compared to respective portions of the reference images.

In step 854, one or more distances to the object 8 are stored. Note thatbased on an amount of deformation to different portions of the pattern,different depth information may be determined. Therefore, step 854 maystore different depth information for different part of the object 8. Inoptional step 808, a 3D map of the object 8 is generated based on thedata stored in step 854.

FIG. 9 is a flowchart of one embodiment of a process 900 of generating areference image. The depth camera 20 that generates that reference imagemay have a linear array detector 504 b to perform process 900; however,that is not required. The reference image may be used in step 852 ofprocess 850. In step 902, a pattern is raster scanned onto an object 8at a known distance from the depth camera. In one embodiment, thepattern is a structured pattern such as a grid or other known pattern.

In step 904, an image that reflects from the reference object 8 isdetected at the linear array detector 504 b. Note that detecting thereference image may include detecting many different scan lines. Forexample, if detecting a known pattern such as a grid, then data thatcorresponds to many different scan lines may be collected. In step 906,a reference image is stored. Process 900 may be repeated for referenceobjects 8 at different known distances from the depth camera. Note thatit may not be necessary to empirically determine the reference images.It may be possible to mathematically determine a model for the referenceimages of hypothetical objects 8 at various distances from the camera.For example, when working with a known pattern such as a grid, it may bepossible to mathematically determine reference images.

The foregoing detailed description of the technology herein has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the technology to the precise formdisclosed. Many modifications and variations are possible in light ofthe above teaching. The described embodiments were chosen to bestexplain the principles of the technology and its practical applicationto thereby enable others skilled in the art to best utilize thetechnology in various embodiments and with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the technology be defined by the claims appended hereto.

We claim:
 1. A depth camera, comprising: a point light source configured to emit a point of light; a raster scanning element configured to optically communicate with the point light source; logic configured to control the raster scanning element to raster scan the point of light from the point light source in a raster scanned pattern over a field of view of the depth camera, wherein only one point of the raster scanned pattern is projected in the field of view at any one time by the point light source; a light detector configured to receive reflected images of the raster scanned light from an object within the field of view, the reflected images including at least a portion of the raster scanned pattern; and logic configured to determine a distance from the depth camera to the object based on apparent deformation in the raster scanned pattern in the reflected images.
 2. The depth camera of claim 1, wherein the deformation is a warping in the raster scanned pattern.
 3. The depth camera of claim 1, wherein the pattern is a grid or stripe pattern, the logic that is configured to determine a distance is configured to determine a distance to the object by comparing spatial differences between received images of the grid or stripe pattern and a plurality of reference images, each of the reference images is an image that would result by raster scanning the grid or stripe pattern over a reference object at different known distances from the depth camera, each reference image contains an amount and a nature of deformation for the respective distance.
 4. The depth camera of claim 1, wherein the light detector is off axis from the scanning element such that a parallax effect causes the apparent deformation of the raster scanned pattern from the vantage point of the light detector.
 5. The depth camera of claim 1, wherein the logic is configured to scan the raster scanned pattern across the field of view such that all energy of the point of light is concentrated on a small point in the field of view.
 6. The depth camera of claim 1, wherein an axis of illumination of the scanned light is aligned with an image axis of the reflected image.
 7. The depth camera of claim 1, wherein the pattern is a grid or stripe pattern, the logic that is configured to determine a distance is configured to determine a distance to the object by determining spatial differences between a received image of the grid or stripe pattern and a reference image, the reference image is an image that would result by raster scanning the grid or stripe pattern over a reference object at a known distance from the camera.
 8. The depth camera of claim 1, wherein the distance determination logic is configured to determine a depth image of the object in the field of view.
 9. A method of scanning to determine depth information, the method comprising: transmitting light from a point light source in a camera; controlling a scanning element while transmitting the light to scan the light in a field of view of the camera, including raster scanning a raster scanned pattern in the field of view, wherein only one point of the raster scanned pattern is projected in the field of view at any one time by the point light source; receiving reflected images from an object in the field of view of the camera while controlling the scanning element, the reflected images include at least a portion of the raster scanned pattern; analyzing spatial properties of the received images, the spatial properties including warping in the raster scanned pattern; and determining a distance from the camera to the object based on the warping in the raster scanned pattern.
 10. The method of claim 9, wherein the receiving reflected images is at a linear array detector.
 11. The method of claim 9, wherein an axis of illumination of the scanned light is aligned with an image axis of the reflected image.
 12. The method of claim 9, wherein the controlling a scanning element includes determining how far to raster scan a line based on whether the object has been fully scanned.
 13. The depth camera of claim 9, wherein the controlling a scanning element includes rotating the scanning element to raster scan the light into the field of view.
 14. The method of claim 9, wherein: the determining a distance from the camera to the object comprises determining the distance to the object based on differences between spatial properties of the reflected images and a plurality of reference patterns, the reference patterns are each an image that would result by raster scanning the pattern over a reference object at a known distance from the camera, each reference image contains an amount and a nature of deformation for the respective known distances.
 15. The method of claim 9, wherein raster scanning the raster scanned pattern in the field of view comprises: scanning the raster scanned pattern across the field of view such that all energy of the light from the point light source is concentrated on a small point in the field of view, wherein the received reflected images from the object have a high signal/noise ratio (S/N).
 16. A depth camera, comprising: a point light source configured to emit collimated light; a scanning element configured to optically communicate with the point light source; logic configured to raster scan lines of the collimated light from the point light source in a raster scanned pattern over a field of view of the depth camera, wherein only one point of the raster scanned pattern is projected in the field of view at any one time by the point light source; a light detector configured to receive reflected images of the raster scanned light from an object within the field of view, the reflected images include at least a portion of the raster scanned pattern; logic configured to determine multiple distances from the depth camera to the object based on spatial properties of the reflected images, the logic configured to determine is configured to compare the raster scanned pattern in the reflected images with a plurality of reference images, each of the plurality of reference images is an image that would result by raster scanning the pattern over a reference object at different distances from the depth camera, each reference image contains an amount and a nature of deformation for the respective different distances; and logic configured to generate a 3D mapping of the object based on the multiple distances.
 17. The depth camera of claim 16, wherein the logic is configured to determine an amount of deformation in the raster scanned pattern to determine the multiple distances.
 18. The depth camera of claim 16, wherein the raster scanned pattern is a grid pattern.
 19. The depth camera of claim 16, wherein the raster scanned pattern is a stripe pattern. 